The IMPACT, PLASTIC, and SECCHI instruments on STEREO Ahead were turned off at 16:00 UT on Friday, 20 March 2015 in preparation for superior solar conjunction. On Tuesday, 24 March, also at 16:00 UT, the STEREO Ahead spacecraft will be reset into a "safe mode" that it will remain in for the next several months until normal operations can be resumed again in July.

The term "superior solar conjunction" is the technical phrase which refers to period when one or the other STEREO spacecraft is on the opposite side of the Sun from Earth. For each spacecraft, there is a period when it is so close to the Sun as seen from Earth that the radio interference from the Sun makes it impossible to communicate at all with the spacecraft. For a few days, it will even be physically blocked by the Sun. Without any possibility of communications, the spacecraft will have to be placed into "safe mode" until contact can be reestablished. Before communications are completely cut off, the spacecraft will start slowly rotating about the axis which points at the Sun. This is done to reduce the load on the reaction wheels which keep the spacecraft pointing stabilized. All the science instruments will be turned off, with the sole exception of the radio instrument SWAVES which will stay on to record beacon mode data on the recorder for eventual playback in November 2015. Technical and safety considerations prevent the other instruments from being on during this time.





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